In a headbox of a papermaking machine, a vertical tube bank is located inside the headbox nozzle and distributes a uniform flow of fluid from the headbox delivery system to the headbox nozzle. The vertical tube bank is located between the pond sides and is trapped by the apron support structure and the top of the headbox nozzle. The fluid or stock is accelerated through the vertical slot openings into rectangular chambers located adjacent to one another. The discharge side of the vertical tube bank is nearly 100% open area into the headbox nozzle. The vertical openings provide a more uniform flow distribution requiring less mixing of individual flow streams and a uniform pressure drop across the tube bank which produces a better basis weight profile.
The vertical tube bank is constructed from metallic material. The flow passages in the tube bank are highly polished to prevent fiber from adhering to the surfaces.
In the headbox of the present invention, the tube bank is constructed from multiple segments or is constructed from a single block of material. When constructed from multiple pieces, the tube bank can be welded or glued together. Alternatively, clamping forces are utilized with through bolts to contain the internal forces of the stock pressure. The tube bank is constructed from multiple pieces stacked together to form the vertical tube bank. Multiple distinct sections that change the flow area within the flow chamber are assembled one after the other. The vertical tube bank front and drive side outside flow channels, or multiple front and drive side channels near the front and drive side walls, include a mechanism that alters the flow in these outer slots. This flow alteration provides a tool for controlling fiber orientation.
The tube bundle is fixed in location inside the headbox by locating devices. The vertical tube bank upstream surface has a series of vertical slots located on an equal pitch across the entire length of the tube bank. The width of the vertical slots are designed such that the width of the slot can be easily changed. Changing the slot width changes the velocity of the stock flow entering the tube bank resulting in improved fiber distribution.
The vertical tube bank is designed such that the range of fluid velocities in the initial section of the tube bank is between 3 and 50 feet per second. The exiting velocity range from the vertical tube bank is 1 to 20 feet per second.
The vertical tube bank can be fed from either a cross machine header or multiple flow injection hoses and can be used in combination with a dilution control of the flow leading to the tubebank. When used with a cross machine header, the vertical tube bank segments themselves may contain a series of holes that can deliver dilution control water into the cross machine header. The dilution control water is then transported through multiple holes located vertically between the vertical slots. The dilution water is carried into the next adjacent slot.
More specifically, the headbox apparatus according to the present invention includes the following features:
1. The vertical tube bank minimizes the mixing requirements of multiple individual tubes.
2. The mixing of flows is primarily in the cross machine direction, reducing rotational flows and maximizes cross machine mixing.
3. The vertical tube bank is constructed from one or multiple pieces.
4. The vertical tube bank is constructed with a series of slots on equal or near equal pitch across the entire width of the headbox.
5. The front side and drive side slots include a mechanism to alter the flow rate through these slots either by width or entrance configuration.
6. The vertical slot width can be easily modified to increase or decrease the pressure drop across the tube bank.
7. The vertical tube bank is located inside the headbox in the wet end side of the nozzle between the pond sides, apron support structure and nozzle roof.
8. The vertical tube bank is constructed of multiple MD and CD direction adjacent zones with varying open areas.
9. The vertical tube bank discharge side has greater than 85% open area into the nozzle area of the headbox.
10. The vertical tube bank can be utilized in headboxes where the delivery of fluid to the headbox is completed by means of a tapered header or a multiple tube/hose delivery system.
11. The vertical tube bank is operated in conjunction with a dilution control system or without a dilution control system.
12. The vertical tube bank may contain multiple holes to deliver dilution water through the block and into the tapered header.
More particularly, a conventional headbox distributor uses a tube array to spread the pulp slurry as uniformly as possible across the width of a paper machine headbox prior to the start of the drainage or other thickening process. The tube array is generally made up of individual round inlet tubes mounted is some manner to cause acceleration of the flow into each tube from a cross machine header or other form of supply of the slurry prior to the tube array. The pressure drop from the acceleration of the flow at the inlet of each tube within the array is critical to the uniformity of the flow within each tube and therefore to the uniformity of the cross machine uniformity of the headbox in general. This acceleration of the flow is also a factor in the operational cleanliness of the headbox operation. The exit end of a typical tube array may take on many shapes (round, hexagonal, rectangular or square or other shape) but eventually the flows exiting each individual tube must be re-joined prior to or within the nozzle of the headbox prior to discharge to the drainage area. The reorientation of the round tube entrance flow to the eventual rectangular shape of the nozzle will create disturbances in the flow in all directions. These disturbances must be damped or reduced in some way prior to discharge out the slice so as not to cause nonuniformities in the paper web.
The purpose of the present invention is to create the necessary pressure drop and subsequent uniform cross machine flow distribution using only vertical channels in the flow distributor. This will minimize non-cross machine flow disturbances improving cross machine uniformity of the flow. The use of only vertical channels also improves the cross machine characteristics of the fiber slurry by minimizing non cross machine forces on the fibers by the fluid flow. The design is equally applicable to headboxes using dilution to control the headbox profile or other mechanical profile controls techniques.
Further advantages of this invention are simplicity of manufacturing using easily manufactured turbulence generating devices and improved structural stiffness within the headbox to withstand internal pressures of the fluid flow.
Therefore, the primary feature of the present invention is the provision of a headbox apparatus that overcomes the problems associated with the prior art headboxes and which makes a significant contribution to the papermaking art.
Another feature of the present invention is the provision of a headbox apparatus for a papermaking machine that is easier and less costly to manufacture when compared with prior art headboxes.
A further feature of the present invention is the provision of a headbox apparatus for a papermaking machine that improves mixing of the pulp prior to discharge thereof to a downstream drainage arrangement.
Other features and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description of a preferred embodiment of the present invention contained herein.